Document this parameter to the constructor
diff --git a/docs/primitives/cryptographic-hashes.rst b/docs/primitives/cryptographic-hashes.rst
index d4dde04..aeb30f4 100644
--- a/docs/primitives/cryptographic-hashes.rst
+++ b/docs/primitives/cryptographic-hashes.rst
@@ -1,11 +1,13 @@
Message Digests
===============
-.. class:: cryptography.primitives.hashes.BaseHash
+.. class:: cryptography.primitives.hashes.BaseHash(data=None)
Abstract base class that implements a common interface for all hash
algorithms that follow here.
+ If ``data`` is provided ``update(data)`` is called upon construction.
+
.. method:: update(data)
:param bytes data: The bytes you wish to hash.